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Muscle Rupture in Dogs

A normal muscle can be stretched, pinched, or injured directly, resulting in fiber disruption, weakening, and immediate or delayed separation of the uninjured portions. Normal activity may cause muscle disruption. Alternatively, the muscle structure may be compromised by systemic or iatrogenic (physician-caused) conditions. The rupture may be complete or incomplete, and may be in the middle of the muscle or at the muscle-tendon junction. The acute (sudden and severe) stage is characterized by a typical inflammatory reaction that becomes chronic over time, with cross-linking, and adhesion development over time. Frequently, the acute phase is overlooked, as the signs may be temporary and respond well to rest. The chronic effects are often progressive and unresponsive to support therapies.

The muscles of the limbs, and the chewing muscles are the primary structures affected. Traumatic injury is indiscriminate, though certain activities may predispose because of exposure. The ruptures that are apparently unrelated to trauma seem to affect middle-aged to older working dogs, with no reported gender predilection.

Symptoms and Types

Acute injury

• Immediate lameness that is characterized by the specific muscle affected
• Localized swelling, heat, and pain
• Generally present for a few days to a week
• Chronic phase (if it develops)

Progressive

• Painless
• Usually associated with scar tissue that impedes normal function of an extremity

Causes

• Trauma
• Overextension
• Myositis (inflammation)
• Degenerative (unknown etiology)
• Myopathy (a neuromuscular disease), secondary to medical conditions
• Apparent risk factor for dogs is involvement in hunting, tracking, or similar activities in the outdoors that put stress on the muscles

Diagnosis

Your veterinarian will conduct a thorough physical examination, looking for evidence of neurologic dysfunction and tendon rupture. Diagnostic imaging will include X-rays to look for evidence of bone fragment defects and translocations, and ultrasound to look for swelling and disorientation of the normal muscle fiber at the site of injury in acute cases. Scar tissue and contracted areas of fibrous tissue can be seen in the muscle in chronic cases. Magnetic resonance imaging (MRI) can be used to look for edema and hemorrhage, and to achieve localization of the problem that will help to identify the type of problem.

Your doctor will also test your dog’s joints for evidence of joint instability or malalignment. Measurable differences between normal and abnormal sides may be useful in documenting the affected muscle site. Another thing your doctor can do is conduct a biopsy of the affected muscle to detect the presence of fibrous tissue and loss of muscle cells. Differentiating atrophy due to disuse from neurologic atrophy, and from injury-induced scarring, may be impossible without corroborating evidence.